A conventionally known technology is to change operation power points of photovoltaic cells so as to maximize an amount of power generated by photovoltaic cells. Such a technique is called MPPT (Maximum Power Point Tracking) method (for example, PTL 1).
Also known is a system (hereinafter referred to as EMS: Energy Management System) for controlling an interconnection between photovoltaic cells and a power system. The EMS controls such that power generated by photovoltaic cells is output to the power system side (reverse power flow control), and so forth.
Since the amount of power generated by the photovoltaic cell is affected by weather, information measured by measuring means is used so as to predict the amount of power generated by the photovoltaic cell. It is noted that examples of the measuring means include an actinometer for measuring the amount of solar radiation, a thermometer for measuring air temperature, and a thermocouple for measuring a temperature of photovoltaic cells. As it is preferable to arrange the measuring means close to the photovoltaic cell in these cases, communication means is used so as to transmit the information measured by the measuring means to the EMS.
There are some cases, though, where it is not possible to obtain a power source without any inhibition at an installation site for power supplying means represented by photovoltaic cells. For example, the photovoltaic cell may be installed in a desert.
The inventors, in such cases, conceived of using the power supplying means represented by photovoltaic cells, as a power source for the measuring means and the communication means.
On the other hand, as mentioned above, the amount of power generated by an off-grid power supplying means such as photovoltaic cells is affected by weather. Accordingly, when the power supplying means represented by photovoltaic cells is used as a power source for the measuring means and the communication means, it is impossible to stably supply power to the measuring means and the communication means.